The invention relates to a driver circuit for a matrix display panel. The invention also relates to a display apparatus comprising a matrix display panel.
U.S. Pat. No. 4,896,149 discloses a matrix display panel having a display surface comprising a pattern formed by a rectangular planar array of nominally identical display elements which are mutually spaced apart. Each display element in the array represents the overlapping portions of column or data electrodes arranged in vertical columns, and narrow channels arranged in horizontal rows. The data electrodes are deposited on a major surface of a first electrically non-conductive, optically transparent substrate, and the channels are inscribed in a major surface of a second electrically non-conductive, optically transparent substrate. Each channel is filled with an ionizable gas. Electro-optic material (for example, a nematic liquid crystal) and a thin layer of dielectric material are sandwiched between the two substrates. The dielectric layer functions as a barrier between the ionizable gas and the layer of liquid crystal material. Each display element can be modeled as a capacitor whose top plate represents one of the data electrodes and whose bottom plate represents the free surface of the layer of dielectric material. Each channel comprises a parallel arrangement of a reference electrode and a row electrode. The reference electrodes are connected to a common electric reference potential.
A data driver supplies data signals via output amplifiers as data voltages in parallel with the data electrodes. When a data strobe or select driver supplies a select pulse with sufficient amplitude to the row or select electrode, the gas in the channel assumes an ionized state and becomes conductive (plasma). In this way, a row of display elements associated with this channel is selected. This means that the capacitors are charged with the data voltages. Upon completion of the storage of the data signals, the select driver terminates the voltage pulse and the plasma starts extinguishing. When the plasma has been extinguished, the capacitors are disconnected as the free surface of the layer of dielectric material is floating again. The charge on the capacitors will be stored until the plasma in the channel becomes conductive again. The select electrodes are selected one by one until the entire display surface is completely addressed to store and display an image field of data.
The timing involved in storing a line of data in a row of display elements is explained in the following description. First, the plasma has to be formed after the select electrode receives a select pulse. The plasma formation time may be partly eliminated as a factor in the timing by initiating the select pulse in advance during a preceding line. The data voltages must be present before the plasma starts decaying too much. The data setup time represents the time during which the data driver slews between the data values of two adjacent lines of data. Next, it takes some time for a display element to acquire the presented data voltage. This data capture time depends on the mobility of the plasma ions. The plasma decay time represents the time during which the plasma in the channel returns to a de-ionized state upon removal of the select pulse. The conductivity of the plasma has to decrease to such a value that the crosstalk is sufficiently low when the subsequent data signals are presented to the next row of display elements. The time required to address a row of display elements equals at least the sum of the data setup time, the data capture time, and the plasma decay time.
If high-resolution display information with a high line frequency has to be displayed on such a plasma-addressed liquid crystal (PALC) display, the data setup time, the data capture time, and the plasma decay time have to be minimized. In a practical situation, wherein a line of data has to be stored in 12 μs, a data setup time of 1 to 2 μs is required. Known data drivers show a high dissipation to allow such a short data setup time.